1. Field of the Invention
This invention relates to compositions having a utility as pyrethroid insecticides or as intermediates for the preparation of pyrethroid insecticide esters, ethers, etc.
2. Description of the Prior Art
There are a multitude of patents and literature references relating to the preparation of synthetic pyrethrines containing the cyclopropane ring system and the use of these compounds as insecticidal intermediates. These classes of insecticides have found wide acceptance because of their relative non-toxicity to mammals and their environmental compatability due to lack of persistence.
Various esters and ether derivatives of the pyrethrine class are shown in U.S. Pat. Nos. 3,979,519; 3,973,036; 3,981,903; 3,954,814; 3,927,068; 3,988,380; 4,003,945 and 4,000,181.
One of the previous methods for synthesizing the cyclopropane derivatives is known as the Staudinger process. It involves the reaction of ethyldiazoacetate and dimethylhexadiene to form the resulting carboxylate ester.
The halovinyl class of pyrethrines, which are more potent than the nonhalogen substituted compounds, can be also formed by the Staudinger process. This class is made by reacting ethyldiazoacetate with a compound such as 1,1-dichloro-4-methyl-1,3-pentadiene and then saponifying the resulting ester. The problems with the Staudinger process are: the diazoester is unstable (often explosive) and the diazo ester is suspected of being carcinogenic, thus making it a difficult process to handle on a large scale.
Recently, an improved process for preparing halosubstituted vinylcyclopropane carboxylates has been disclosed in Belgian Patent 833,278. In that patent, prenyl alcohol is condensed with an ortho ester, namely ethyl orthoacetate to form a gamma unsaturated carboxylate. The carboxylate then is reacted with a polyhalomethane, e.g. carbon tetrachloride to form a gamma-halo carboxylate which is followed by dehydrohalogenation and cyclization to bring about the formation of dihalovinyl cyclopropane carboxylate.
Another route based quite similarly to that disclosed in the Belgian patent comprises reacting an acetoacetic ester with ethanol to give the ethyl vinylether of an acetoacetic ester. Then the resulting ester is transetherified with prenyl alcohol to give an allyl vinyl ether of an acetoacetic ester, which thermally rearranges and decarboxylates to a gamma methylvinylketone. This ketone can then undergo polyhalomethane addition, and dehydrohalogenation and cyclization to give the product. One advantage of this process is that the ketone product can be oxidized in such a way to provide selectivity to the trans or cis isomer.
In a recent West German Offenlegungschrift, viz, 26 06 635, a process was disclosed relating to a method for producing dimethyl dichlorovinyl cyclopropane carboxylic acid derivatives. An exemplary acid derivative is prepared by reacting carbon tetrachloride with an olefin, i.e., dimethyl-propane-malonic acid diethyl ester followed by dehydrohalogenation, cyclization and hydrolysis to form the dichlorovinyl cyclopropane dicarboxylic acid (Ex. 3). In the Ex. 3 procedure hydrolysis of the ester to the diacid is effected by the addition of ice-cold hydrochloric acid.